1. Field of the Invention
This invention relates to novel azo compounds, metal complex compounds thereof, water-soluble azo dyes containing the azo compounds or metal complex compounds, and polarizing films having a high degree of polarization, said polarizing films each containing as a dichroic dyestuff one of the dyes in an oriented state in a polymer film.
2. Description of the Related Art
It is now the common practice to produce a polarizing film by impregnating a stretched and oriented film of polyvinyl alcohol or a derivative thereof or an oriented film of a polyene with iodine or a dichroic dye as a polarizing element to dye the former with the latter.
Among such polarizing films, those making use of iodine as a polarizing element are excellent in initial polarizing ability but are weak against water or heat. They are hence accompanied by a problem in durability when employed over a long period of time under high temperature and humidity conditions. To improve their durability, it has been proposed, for example, to intensify their treatment in an aqueous solution containing formaldehyde or boric acid or to use, as a protective film, a polymer film having low moisture permeability. Their durability is however still insufficient under high temperature and moisture conditions.
Polarizing films making use of a dichroic dye as a polarizing element, compared with polarizing films using iodine, have better resistance against water and heat but inferior in polarizing ability. With a view toward improving this drawback, polarizing films using an organic dye as a polarizing element and improved in heat resistance are proposed in Japanese Patent Laid-Open Nos. 153648/1979, 145255/1984, 156759/1985, 168743/1985, 68902/1991 and 89203/1991, but they are not fully satisfactory in polarizing performance.
There is hence a strong demand for the development of dye-base polarizing films which are superior in polarizing performance to iodine-base polarizing films.